The present invention relates to a method for inspecting completely hermetically sealed packages, such as food and medical consumption articles, for any pinholes.
Today, hermetically sealed packaging is used in a variety of commodities including food and medical consumption articles such as physiological saline to keep their contents in a sterilized state. In the case of food, the presence of pinholes would cause the contents of the package to contact the air, resulting in deterioration or rot. Also, in the case of medical consumption articles, for example, transfusion bottles, the presence of pinholes would cause contamination or deterioration. Thus, the pinhole inspection for these hermetically sealed packages is of great importance. Conventionally, this pinhole inspection would be carried out in the following method. That is, because a hermetically sealed package does not allow an electrode to be penetrated thereinto, for example in the case of food, a metal pin is stuck into a completed package and taken as one electrode so as to serve as an opposed electrode to an external electrode set in contact with the package. In this state, with a high voltage applied between the two electrodes, the hermetically sealed package is inspected for pinholes, and after the inspection, any pinholes are hermetically sealed in a different process. However, this inspection method has had a drawback that the inspection process would be complicated, requiring a subsequent process of closing the pinholes. A method for pinhole inspection which solves this drawback and which allows a pinhole inspection to be done without damaging the completed hermetically sealed package has been disclosed in, for example, Japanese Patent Publication SHO 50-6998. In this method, a food hermetically sealed by a package made from an electrically insulating film is sandwiched between a pair of electrodes, and a voltage is applied between both electrodes so as to give a large difference between capacitances that are formed between the individual electrodes and the food, respectively. Then, a current which is generated by a spark between one of the electrodes and the food is detected, by which any pinhole is detected.
When the presence or absence of any pinhole is detected by detecting a short-time current generated by a spark as described above, it would be the actual case in terms of practical work that the presence or absence of pin holes is detected by a change (magnitude) of the detected current. In this case, applying a voltage between the two electrodes that sandwich the hermetically sealed package would cause a leakage current or charging current to necessarily flow regardless of the presence or absence of pinholes. This phenomenon is more likely to occur particularly with higher voltage, and is also affected by weather such as humidity and temperature of the periphery of the inspection object, which forms the atmosphere during the inspection, where the leakage current becomes larger under the conditions of rain or high humidity. Further, there may arise an error to the current at the detection point due to some influence of floating fine dusts or the like. As a result, the decision as to the presence or absence of pinholes by the magnitude of the short-time current could not be free from misoperations such as a decision of the presence of a pinhole notwithstanding the absence of any pinhole.
The present applicant has previously proposed an inspection method in Japanese Patent Applications HEI 8-53816 and HEI 10-158569. In this method, the hermetically sealed package is placed on a support electrode of a specified configuration, such as a grounded electrode plate, with side face portion of the hermetically sealed package put into contact with the support electrode, and a DC high voltage is applied between the support electrode and an electrode put into close contact with or opposed proximity to an inspection-object end portion of the hermetically sealed package so that the contents of the hermetically sealed package are electrically charged. Then, with the support electrode either released from grounding or kept grounded, the electrode put into contact with the inspection-object end portion is grounded, where a discharge current from the inspection-object end portion is detected, by which any pinhole of the hermetically sealed package is detected.
This method has made it possible to efficiently inspect a hermetically sealed package for the presence or absence of any pinholes by an inspection of the inspection-object end portion at a site where pinholes are most likely to occur while misoperations are fully prevented during the inspection of pinholes of the hermetically sealed package. However, the method has still required a sequence of inspection procedure.
The present invention has been accomplished in view of these and other problems. An object of the present invention is therefore to provide an efficient method for inspecting a hermetically sealed package which method allows the inspection to be achieved with further simpler procedure and which is fully prevented from occurrences of misoperations due to the atmosphere during the inspection.
For this method, the hermetically sealed package to be inspected can be exemplified, in the field of food, principally by cylindrical-shaped packages such as sausage hermetically sealed and packaged in unit pieces, and besides retort foods packed in a flat bag made of plastic film. In the field of medical consumption articles, the hermetically sealed package can be exemplified by blood preparations such as transfusion blood and blood plasmas contained in a plastic bag in addition to transfusion agents such as physiological saline or Ringer""s solution contained in a transfusion bottle also made of plastic as the inspection object for prevention of contamination and deterioration of the contents due to contact with outside air via pinholes. Furthermore, hermetically sealed packages in which a particle or powder conductive material such as cooked rice or solid-matter iron powder is hermetically sealed in a plastic bag also can be an object of inspection as well.
In order to achieve the above object, the present invention provides a method for inspecting any pinholes of a hermetically sealed package 3 in which contents 1 such as electrically conductive fluid or powder or food are covered with an electrically insulating film 2, the method comprising steps of: putting a single electrode 4 derived from a voltage output terminal of a high voltage power supply 6 into contact with or proximity to a side face portion 3, of the hermetically sealed package 3 so that the contents 1 in the hermetically sealed package 3 are electrified; then grounding an electrode 5 put into close contact with or opposed proximity to an inspection-object portion 3a of the hermetically sealed package 3; and detecting a discharge current from the inspection-object portion 3a to thereby detect any pinhole of the hermetically sealed package 3. In this method, the electrode 5 may be implemented by electrically conductive liquid or electrically conductive gel.
With such a method, when the single electrode 4 derived from the voltage output terminal of the high voltage power supply 6 is put into contact with or proximity to the side face portion 31 of the hermetically sealed package 3, the electrically conductive contents 1 within the hermetically sealed package 3 are electrified by a negative or positive potential of the high voltage (0.6 kV-30 kV) applied to the electrode 4, so that negative (xe2x88x92) ions or positive (+) ions are generated.
Next, upon the grouping of the electrode 5 put into close contact with or opposed proximity to the inspection-target portion 3a of the hermetically sealed package 3, in the case where a pinhole is present at the inspection-object end portion 3a, if negative (xe2x88x92) ions are generated in the contents 1, the negative (xe2x88x92) ions gather to the pinhole and negative (xe2x88x92) electrons within the negative (xe2x88x92) ions collectively flow through the pinhole toward the ground (earth), so that the negative charges are lost, thus resulting in discharge. On the other hand, if positive (+) ions are generated in the contents 1, the positive (+) ions gather to the pinhole and positive charges are lost by negative (xe2x88x92) electrons flowing from the ground side through the pinhole, thus resulting in discharge. Without any pinhole, negative (xe2x88x92) electrons in the negative (xe2x88x92) ions do not flow toward the ground, and the negative (xe2x88x92) ions do not flow from the ground side against the positive (+) ions, go the charges of the contents are not discharged.
Therefore, any pinhole at the inspection-object portion can be detected by detecting the resulting discharge current, where the discharge current could not be detected without the presence of any pinhole at the inspection-object portion 3a. Also, without any pinhole, although the contents 1 are electrified, the electricity is discharged little by little like static electricity so that the electrification dissipates.
In this detection, any pinhole can be detected without errors, irrespective of the atmosphere during the inspection, where the decision is made not by any change (magnitude) of the charging current but by the presence or absence of a discharge current due to the presence or absence of a pinhole at the inspection-object portion 3a (where pinholes are most likely to occur).
Furthermore, as the electrode to be used for electrification of the contents, a single electrode derived from the high voltage output side of the high voltage power supply may be used without requiring a pair of electrodes as would be involved in the prior art.
A DC high voltage power supply may properly be used as the high voltage power supply 6. As the electrode 4 derived from the voltage output terminal of this DC high voltage power supply 6, it is effective to use an electrical conductor which can freely be put into contact with or proximity to the side face portion 31 of the hermetically sealed package 3.
An AC high voltage power supply may also be used as the high voltage power supply 6. In this case, it is desirable to use, as the electrode 4 derived from the high voltage output terminal of this AC high voltage power supply 6, a support electrode which allows the hermetically sealed package to be placed thereon with the side face portion 31 of the hermetically sealed package put into contact with the support electrode, so that discharge through any pinhole from electric charges of the contents that are electrified positively (+) and negatively (xe2x88x92) alternately can be detected by a discharge current detecting device.
Use of an AC high voltage power supply as the high voltage power supply is advantageous in that repetitive inspections are enabled, as compared with the use of a DC high voltage power supply. The reason of this is that, when charges with which the contents are electrified are discharged through a pinhole to a number of times with the use of DC current, some contents become less likely to discharge after some times of discharge, but use of AC current is free from such occurrence.
Another advantage is that, after the product inspection, whereas the remaining charges discharge gradually in the case of DC current, the product, which has been repetitively electrified positively (+) and negatively (xe2x88x92) alternately, does not remain electrified in the case of AC current. Moreover, the greatest advantage is that the need for a rectifier device for converting AC current into DC current is eliminated, allowing the product to be offered inexpensively.
Furthermore, as the electrode 5, electrically conductive rubber or electrically conductive plastic formed so that the electrode 5 can be put into close contact with the inspection-object portion 3a may be used. That is, in the case where the inspection-object portion 3a is provided by a die-molding product of mass production, or in other like cases, the inspection-object portion 3a maintains constant or generally constant in shape, so that the electrode 5 can be easily put into close contact with the surface of the inspection-object portion by taking advantage of the elasticity of this electrically conductive rubber or electrically conductive plastic.